Multispectral imaging scanners are commonly mounted on moving aircraft or satellites for the purpose of recording images of earth terrain as they pass over the earth's surface. The images are recorded as data which consist of a series of scan lines whose relative orientation with respect to other scan lines may change as the aircraft or spacecraft moves along its line of flight. The attitude of aircraft and spacecraft is subjected to perturbations induced by roll, pitch, yaw, altitude, and velocity changes which introduce non-systematic geometric distortions into the image of the terrain. In the case of aircraft, such perturbations result from wind buffeting, changes in air density and inadvertent course changes. Perturbations in a satellite environment are more subtle, but can also result from atmospheric buffeting (in low altitude orbit), orbital control maneuvers, and changes in the satellite's center of mass (i.e. fuel consumption, antenna and solar array orientation changes).
In order to correct the geometry of the "raw" image data, it is usually possible to identify pixels with ground control points on maps for every few scan lines in the image data by searching maps for the exact location of features which are distinct pixels (picture elements) in the image data, then mathematically warping and resampling the entire image to arrive at the best fit for all the ground control points. However, this approach is especially expensive in terms of the time and labor required to manually correlate the recorded image data with the position of ground control points, and the correction relies exclusively upon the accuracy and density of the ground control. Another solution to this problem involves horizon seekers, star pointers and inertial navigation systems on-board the spacecraft or aircraft. These attitude sensors detect and record attitude change data required for the partial geometric correction of image data. Such data is not optimal for at least three reasons: first, they use features or inertial references which are not an intrinsic part of the recorded terrain data; second, they can cost as much as the primary sensor; and third, their weight and power consumption may be prohibitive for some applications.
Consequently, there is a need in the art for a lightweight, more efficient, and less expensive system for detecting and recording the attitude changes of a platform, such as an imaging sensor platform, which can be used either for aircraft or satellite terrain image sensor applications.